/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * JSONLoader.java
 * Copyright (C) 2009-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core.converters;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import java.util.zip.GZIPInputStream;

import weka.core.Instance;
import weka.core.Instances;
import weka.core.json.JSONInstances;
import weka.core.json.JSONNode;

/**
 * <!-- globalinfo-start --> Reads a source that is in the JSON format.<br/>
 * It automatically decompresses the data if the extension is '.json.gz'.<br/>
 * <br/>
 * For more information, see JSON homepage:<br/>
 * http://www.json.org/
 * <p/>
 * <!-- globalinfo-end -->
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 * @version $Revision$
 * @see Loader
 */
public class JSONLoader extends AbstractFileLoader implements BatchConverter, URLSourcedLoader {

    /** for serialization. */
    private static final long serialVersionUID = 3764533621135196582L;

    /** the file extension. */
    public static String FILE_EXTENSION = ".json";

    /** the extension for compressed files. */
    public static String FILE_EXTENSION_COMPRESSED = FILE_EXTENSION + ".gz";

    /** the url. */
    protected String m_URL = "http://";

    /** The reader for the source file. */
    protected transient Reader m_sourceReader = null;

    /** the loaded JSON object. */
    protected JSONNode m_JSON;

    /**
     * Returns a string describing this Loader.
     * 
     * @return a description of the Loader suitable for displaying in the
     *         explorer/experimenter gui
     */
    public String globalInfo() {
        return "Reads a source that is in the JSON format.\n" + "It automatically decompresses the data if the extension is '" + FILE_EXTENSION_COMPRESSED + "'.\n\n" + "For more information, see JSON homepage:\n" + "http://www.json.org/";
    }

    /**
     * Get the file extension used for JSON files.
     *
     * @return the file extension
     */
    public String getFileExtension() {
        return FILE_EXTENSION;
    }

    /**
     * Gets all the file extensions used for this type of file.
     *
     * @return the file extensions
     */
    public String[] getFileExtensions() {
        return new String[] { FILE_EXTENSION, FILE_EXTENSION_COMPRESSED };
    }

    /**
     * Returns a description of the file type.
     *
     * @return a short file description
     */
    public String getFileDescription() {
        return "JSON Instances files";
    }

    /**
     * Resets the Loader ready to read a new data set.
     * 
     * @throws IOException if something goes wrong
     */
    public void reset() throws IOException {
        m_structure = null;
        m_JSON = null;

        setRetrieval(NONE);

        if (m_File != null) {
            setFile(new File(m_File));
        } else if ((m_URL != null) && !m_URL.equals("http://")) {
            setURL(m_URL);
        }
    }

    /**
     * Resets the Loader object and sets the source of the data set to be the
     * supplied File object.
     *
     * @param file the source file.
     * @throws IOException if an error occurs
     */
    public void setSource(File file) throws IOException {
        m_structure = null;
        m_JSON = null;

        setRetrieval(NONE);

        if (file == null)
            throw new IOException("Source file object is null!");

        try {
            if (file.getName().endsWith(FILE_EXTENSION_COMPRESSED))
                setSource(new GZIPInputStream(new FileInputStream(file)));
            else
                setSource(new FileInputStream(file));
        } catch (FileNotFoundException ex) {
            throw new IOException("File not found");
        }

        m_sourceFile = file;
        m_File = file.getAbsolutePath();
    }

    /**
     * Resets the Loader object and sets the source of the data set to be the
     * supplied url.
     *
     * @param url the source url.
     * @throws IOException if an error occurs
     */
    public void setSource(URL url) throws IOException {
        m_structure = null;
        m_JSON = null;

        setRetrieval(NONE);

        setSource(url.openStream());

        m_URL = url.toString();
    }

    /**
     * Set the url to load from.
     *
     * @param url the url to load from
     * @throws IOException if the url can't be set.
     */
    public void setURL(String url) throws IOException {
        m_URL = url;
        setSource(new URL(url));
    }

    /**
     * Return the current url.
     *
     * @return the current url
     */
    public String retrieveURL() {
        return m_URL;
    }

    /**
     * Resets the Loader object and sets the source of the data set to be the
     * supplied InputStream.
     *
     * @param in the source InputStream.
     * @throws IOException if initialization of reader fails.
     */
    public void setSource(InputStream in) throws IOException {
        m_File = (new File(System.getProperty("user.dir"))).getAbsolutePath();
        m_URL = "http://";

        m_sourceReader = new BufferedReader(new InputStreamReader(in));
    }

    /**
     * Determines and returns (if possible) the structure (internally the header) of
     * the data set as an empty set of instances.
     *
     * @return the structure of the data set as an empty set of Instances
     * @throws IOException if an error occurs
     */
    public Instances getStructure() throws IOException {
        if (m_sourceReader == null)
            throw new IOException("No source has been specified");

        if (m_structure == null) {
            try {
                m_JSON = JSONNode.read(m_sourceReader);
                m_structure = new Instances(JSONInstances.toHeader(m_JSON), 0);
            } catch (IOException ioe) {
                // just re-throw it
                throw ioe;
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        return new Instances(m_structure, 0);
    }

    /**
     * Return the full data set. If the structure hasn't yet been determined by a
     * call to getStructure then method should do so before processing the rest of
     * the data set.
     *
     * @return the structure of the data set as an empty set of Instances
     * @throws IOException if there is no source or parsing fails
     */
    public Instances getDataSet() throws IOException {
        if (m_sourceReader == null)
            throw new IOException("No source has been specified");

        if (getRetrieval() == INCREMENTAL)
            throw new IOException("Cannot mix getting Instances in both incremental and batch modes");

        setRetrieval(BATCH);
        if (m_structure == null)
            getStructure();

        try {
            // close the stream
            m_sourceReader.close();
        } catch (Exception ex) {
        }

        return JSONInstances.toInstances(m_JSON);
    }

    /**
     * JSONLoader is unable to process a data set incrementally.
     *
     * @param structure ignored
     * @return never returns without throwing an exception
     * @throws IOException always. JSONLoader is unable to process a data set
     *                     incrementally.
     */
    public Instance getNextInstance(Instances structure) throws IOException {
        throw new IOException("JSONLoader can't read data sets incrementally.");
    }

    /**
     * Main method.
     *
     * @param args should contain the name of an input file.
     */
    public static void main(String[] args) {
        runFileLoader(new JSONLoader(), args);
    }
}
